More control over output results by providing ResultCollector and output filters

[fesor]

Currently stepler uses step execution results as output provider without any processing (only json_encode in controller which is not so flexible).

What can be done is that we can add ResultCollector component, which will support custom filters for step results and so on:

class FeatureContext implements KernelAwareInterface, ResultCollectorAware
{

    public function setResultCollector(ResultCollector $results)
    {
          $this->results = $results;

          $this->results->resultsProcessor(function ($result, array $options) {
              // options can be used for configuring JMS serializer context or something like that.
              return $this->container->get('jms_serailizer')->serialize($result);
          });
    }

    /**
     * @Givne I have registered user
     * @CollectResult(options={"groups": {"profile", "friends"}})
     */
    function iHaveRegisteredUser()
    {
         $user = $this->container->get('user_registrator')->registerUser();

         return $user;
    }
}

Also it would be nice to collect all results by default with ability to register custom filters in config...